The present invention relates to a method for detecting a turning situation with a view, notably, to generating a setpoint for a transmission of an automobile vehicle drive train. It also relates to a device implementing such a detection method.
An automobile vehicle automatic transmission conventionally comprises a control unit receiving one or more input parameters representing, amongst others, the state of the road: slope, change of slope, curvature, etc. Then, depending on the values of these parameters, the control unit delivers a transmission ratio setpoint to be applied, with interposition, where necessary, of “disable” commands temporarily prohibiting gear-ratio up-shift or down-shift changes for an enhanced driving comfort, for example in certain cases where the vehicle is in a turning situation. In a turning phase, a driver driving an automobile vehicle equipped with a conventional automatic transmission is indeed subjected to uncomfortable driving situations.
For example, going into a turn, the driver generally releases the accelerator pedal. The automatic gearbox that was initially on a given ratio then goes directly to the higher ratio owing to the conventional gear-change rules for an automatic gearbox. The vehicle thus no longer benefits from the engine braking effect. The switch to a higher gear ratio then causes an unpleasant swerving sensation for the automobile vehicle.
Methods and associated devices are already known from the prior art that allow adaptations to be applied to try and improve the comfort of the driver and the passengers in a turning phase.
The patent FR 2 779 793 filed by the applicant describes a system for automatic adaptation of a vehicle gearbox in a turning situation. The system detects a turning situation according to the transverse acceleration of the vehicle, then adapts the gear ratio change strategy as a function of the engine speed and the resistive forces applied to the vehicle.
The transverse acceleration may be determined either by accelerometers or calculated from the rotational speeds of a right and of a left non-driven wheel of the vehicle, such as described in the patent FR 2802 646 filed by the applicant. The calculation proposed by the patent FR 2802 646 assumes that the wheels adhere to the road without slipping and therefore requires the speed sensors to measure the rotation of non-driven wheels of the vehicle.
The patent GB 2 381 873 (Robert Bosch GmbH) involves the simultaneous use of a transverse acceleration calculation from the speeds of the wheels of the vehicles, and the results of measurement from a transverse accelerometer, in order to evaluate the transverse acceleration with more reliability. This patent proposes that the values of transverse acceleration exceeding a predefined threshold are put aside as non-valid, that this acceleration comes from the accelerometer measurement or deduced from the speeds of the wheels. This patent proposes that the interpretation of the transverse acceleration be suspended in the case of excessive skidding, defined by a wheel speed on the inside of the turning circle greater than the forward speed of the vehicle, or by a wheel speed on the outside of the turning circle less than the forward speed of the vehicle. This method requires the simultaneous presence of wheel speed sensors and of a transverse accelerometer, with the associated costs and operational issues.